This invention relates to misconvergence measuring apparatus suitable for use in automatic convergence adjustment in the production of color Braun tubes or color display apparatuses using color Braun tubes.
The process of producing color Braun tubes or color display apparatuses using Braun tubes includes the operation of color adjustment in which for the reproduction of the original color the electron beams for the three primary colors are adjusted to be converged over all the display screen. This adjustment is usually called the convergence adjustment.
The automation of the convergence adjustment operation was published in, for example, the Institute of Electronics and Communication Engineers of Japan, Technical Report IE 77-72, 1978, titled "Development of Color Braun Tube Purity Convergence Automatic Adjustment Apparatus".
In this report, a cross-hatched test pattern supplied to a color Braun tube is colored in red, blue and green in turn by switching the cathodes of the color Braun tube, and the displayed images of the test pattern are projected in a camera where the amount of color shift of the images, or the amount of misconvergence, is measured from the time difference from the synchronizing signal to the longitudinal or lateral detection signal. Also, in this report, the purity of the image on the Braun tube is decided from whether a uniform primary color raster can be obtained on the whole screen under the condition that any one of the electron beams of red, blue and green is emitted.
However, the apparatus used in measurement is large-sized and very expensive.
By the way, a small amount of color shift (misconvergence) is measured on the large fluorescent screen of a color Braun tube and the conventional measuring apparatus is large-sized. Therefore, the misconvergence is still at present measured with the eye.
For example, if a lattice-like white line is projected on the screen of the color Braun tube, the presence of a color shift will sometimes divide the white line into a red line on one side and green and blue lines on the other side. Thus, the color shift, or the amount of misconvergence, is measured with the human eye.
The prior art needs an expensive and large-sized system and a large space for the automatic measurement of misconvergence. Also, it requires skilled operators, and because of the need for hands, the problem with labor conditions occurs.
Moreover, in the prior art, the maximum output detection adjustment in the color Braun tube is made by adjusting the focus potential to the color Braun tube so as to achieve the most sharp image of lattice stripes or dots while the displayed image on the color Braun tube operated under predetermined conditions is observed with the eye.
In the prior art, however, the adjustment setting greatly depends on the operator's eyes. Moreover, for the color Braun tubes to be used in computers and other information equipment, the maximum output detection adjustment must consider fine lines and points on the screen because fine patterns and letters are displayed thereon, and, therefore a labor sanitory problem is encountered.